I first had to explore alternatives to a bit after I bought a coming-2yo Thoroughbred filly back in early 1979. A so-called trainer had broken the front of her upper jaw trying to force her into his trailer to go to an all-ages sale as a yearling and it had healed untreated. No way could she wear a bit comfortably.

She was the one who chose eventing as her eventual career. For the dressage phase she and I finally found she could tolerate a Nathe snaffle with a plain cavesson and extremely light contact. I initially hung it in her mouth on a very loose headstall, no reins, and let her show me where she wanted to carry it. For cross country and stadium, she went in something very similar to this.

She also had a very deep, narrow lower jaw and low palate, and was one of those anomalous mares with all four canine teeth. I doubt she would have found many bits comfortable even if her jaw hadn't been broken.

Now I just prefer bitless because the horses prefer it. My young gelding is extremely light in Margo's old noseband, or even just a neck rope and no bridle.